In the prior art, agricultural vehicles are known, for example, tractors or haulers, but also loader vehicles, such as telehandlers, which have hitch systems on which various attachments can be attached for performing a wide variety of tasks. Such a hitch could be arranged both on the back and also on the front. Often, it is necessary or useful to equip the attachments with a specified contact pressure on the ground, in order to operate the attachment and the vehicle at an optimized overall efficiency in their interaction. This contact pressure can involve weight being transferred selectively from the vehicle to the attachment or vice versa.
Furthermore, a hitch is known that moves slowly upward from the ground at a specified pressure, that is, are provided with a so-called floating position function with a contact pressure that can be specified.
Such hitch systems are disclosed, for example, in EP 1 281 872 B1 and DE 10 2004 033 315 A1, wherein the former discloses an electro-hydraulic hitch assembly for an agricultural work machine. The disclosed hitch assembly has available a double-action hydraulic cylinder whose two pressure chambers can be pressurized and can be controlled by means of a suitable control valve, wherein an electro-hydraulic pressure control is provided that detects the pressure by means of pressure sensors in the two pressure chambers and that controls or regulates accordingly.
DE 10 2004 033 315 A1 also discloses a hitch system with double-action hitch cylinders and a pressurized volume flow control means, wherein a pressure-limiting valve is provided through which a maximum pressure in the hydraulic system is controlled as a function of operating states of the hitch assembly or the attachment.
The systems known from the prior art have in common that they can be used as control parameters for the pressure in the working cylinder of the front power lift and therefore certain operating states can be taken into account not at all or only insufficiently for the contact pressure regulation of the hitch. Thus, with conventional contact pressure regulators, often it can be recognized only with difficulty that, for example, the attachment is no longer located on the ground. Another disadvantageous state or a case that can be detected only with difficulty is created, for example, when the vehicle loses contact with the ground or a limit in this respect is reached due to too high a contact pressure of the attachment on an axle.